564 



Dr. Gwilym Owen on the Production of 



nuclei are aggregations, not of water-molecules but of air- 

 molecules, brought into existence by the approach o£ the gas 

 to its condensing point ; in other words, that the nuclei 

 afford evidence of the occurence of incipient liquefaction in a 

 gas at a temperature well above its real liquefying point. 



An experiment to decide definitely between these two views 

 would appear to be impossible, for a perfectly dry gas has 

 probably never been obtained. The present note, however, 

 contains a brief account of a further attempt to eliminate 

 traces of water- vapour from the gas experimented upon. 

 The result obtained supports the view that the nuclei are 

 a o- a relations of air-molecules. 



Owen and Hughes (loc. cit.) obtained their dry air from 

 boiling liquid air. The same method was adopted in the 

 present experiment, with this difference — that the air so 

 obtained was sealed up in contact with P 2 5 for several 

 weeks before it was subjected to the cooling process. The 

 amount of water-vapour ultimately left in a closed space 

 containing P 2 0, 5 is generally regarded as being extremely 

 small. This method of drying a gas is, for example, sufficiently 

 effective to stop entirely several chemical actions requiring 

 the merest trace of moisture, such as the combination of 

 hydrogen and chlorine under the influence of light. 



The arrangement used in the present experiment is shown 

 in the figure. The air to be cooled was contained in the 





W 



glass bulb F some 5 cms. in diameter, connected by a wide 

 tube to a second bulb E, which served to hold the P 2 O r ,. 

 The globe H is the cloud-chamber, connected to a Wilson 

 expansion apparatus, and in which the air is tested for the 



